Glial fibrillary acidic protein (GFAP) is a structural protein found almost exclusively in astrocytes. Our laboratory recently found that mutations in the coding region of the GFAP gene cause Alexander disease (AxD), a rare but usually fatal disorder of the central nervous system. This disease is characterized by the presence of protein aggregates which have GFAP as a primary constituent. The purpose of this proposal is to develop additional information about the mechanism by which the GFAP mutations cause AxD. In Aim 1 we will determine the composition of the RFs to obtain clues for the disease mechanism, an approach that has proved fruitful for other protein aggregate disorders. The aggregates will be partially purified, and their protein components identified by mass spectrometry. In Aim 2 we will determine if the GFAP is abnormally deiminated or phosphorylated, two modifications of GFAP known to affect its polymerization and to be present in other neurodegenerative disorders. In Aim 3 we will also determine whether the mutant form specifically accumulates in the aggregates. This will test the hypothesis that mutant GFAP is not toxic per se, but produces disease by causing GFAP accumulation.